Spatial and Temporal Distribution of Cownose Rays (Rhinoptera bonasus) in North Carolina
Vicky Fong
https://github.com/vfong3/Fong_ENV872_FinalProject
Rationale and Research Questions
Fever of cownose rays swimming near the surface. (Image credit:
Chesapeake Bay Journal) 
Cownose rays (Rhinoptera bonasus) are considered a ‘Vulnerable’ species by the IUCN Red List globally due to over-fishing (Carlson et al. 2020). In the United States specifically, cownose rays have had a long history of negative interactions with commercial shellfish industries, specifically oyster aquaculture in the Chesapeake Bay, Maryland and bay scallop fisheries in North Carolina (NC Division of Marine Fisheries 2007). This conflict was further exacerbated by a study published in 2007 claiming that top-down predation release was responsible for shellfish decline (Myers et al. 2007), which led to the formation of “Save the Bay, Eat a Ray” campaigns to facilitate recovery of oyster populations in Chesapeake Bay. In 2016, Grubbs et al. rebutted the trophic cascade and the implication that cownose rays caused the collapse of shellfish populations, warning the risk of overexploitation of the slow-reproducing species.
Dead cownose rays from “Save the Bay, Eat a Ray” campaigns.
(Image credit: Discover Magazine)
This project aims to investigate the temporal and spatial distribution of cownose rays in North Carolina using open-source data. North Carolina was chosen as the study location as there has been minimal research on cownose rays in the state. The only recent study found higher occurences of cownose rays in late spring and summer months between 2004 and 2006 (Goodman et al. 2010), but no follow-up work has been conducted. This project will investigate the following questions: 1. What is the temporal distribution of cownose rays in North Carolina? 1a. What are the annual trends? Did sightings increase after “Save the Bay, Eat a Ray” campaigns were no longer encouraged following the 2016 study? 1b. What are the seasonal trends? 2. What is the spatial distribution of cownose rays in North Carolina? 2a. Are there seasonal trends in spatial distribution?
Dataset Information
Sightings of cownose rays were obtained from OBIS-SEAMAP (https://seamap.env.duke.edu/), an open-source database for sharks, rays, turtles, seabirds and marine mammals (Halpin et al. 2009). A search for cownose rays resulted in 32,922 records from 66 datasets (government, academic, and private institutions) globally. Since there are no long term studies on cownose rays, these data were collected opportunistically and survey efforts were not standardized.
Table 1. Dataset Information
| Detail | Description |
|---|---|
| Data Source | OBIS-SEAMAP |
| Retrieved From | https://seamap.env.duke.edu/species/160985 |
| Variables Used | latitude, longitude, group_size, date_time |
| Date Range | 2000-2019 |
North Carolina sightings were filtered from the global dataset using the state’s northern (36.588056) and southern (33.843056) latitudinal boundaries. Year, month, and date were extracted from the date_time column, then filtered to only contain sightings since the year 2000. Sightings that did not specify group size were assumed to represent at least one individual and were assigned a group size of 1 as a conservative approach. A cleaned dataset was then created with only the necessary columns for this analysis (latitude, longitude, group_size, date, month, year). The spatial data was provided in the WGS 1984 datum and transformed to UTM Zone 17N for geospatial analysis.
Exploratory Analysis
Initial explorations into the temporal distrbution of cownose rays in North Carolina focused on visualizing the number of sightings by year (Fig. 1) and month (Fig. 2). Initial exploration of spatial distribution mapped the location of each sighting (Map 1).
Figure 1. Number of Cownose Ray Sightings in North
Carolina by Year (2000-2019)
Figure 2. Number of Cownose Ray Sightings in North
Carolina by Month (2000-2019)
Map 1. Locations of Cownose Ray Sightings in North Carolina